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Re: CO2 problems
On Fri, 4 Feb 2000, Frank wrote:
> Hi, thanks to all who answered my previous problem regarding Ph and Co2.
> Your answers raised a lot of questions which I was not sure of. However,
> after several more tests, some of my problems still exist. My Ph now is in
> the range I want, but the Co2 is still way too high. In my first post, I
> neglected to say that I have well water with a Ph of 6.5, a Kh of 3 degrees
> hardness and a Co2 reading of 75 parts per million according to a LaMott test
These pH and KH numbers indicate about 40 ppm CO2 in your well water (this
number is from Pauli Hopea's chart at the Krib). Your original letter
gave us a pH of 6.8 and a KH of 6 at your tap for a CO2 content of 28
ppm. Do you add something to your well water that could account for the
difference in KH?
In your original letter you said the pH in your tanks rose to 8 when you
turned off the CO2. This is all very consistent with your well water
being charged with CO2, and your CO2 injection maintaining CO2 at a
relatively high value. When you stop injecting the CO2 the pH goes up.
That's a normal result of the CO2 level dropping off.
> And, yes, that combination does do a number on my copper pipes.
You should be aware that copper in sufficient concentrations can be toxic
to plants and fish. Copper toxicity could actually explain your lack of
> The Ph
> in my 70 gallon tank is now 6.6, the Kh is 4 degrees hardness, and the Co2 is
> so high I stopped adding reagent after 150 parts per million.According to the
> chart on the krib, my Co2 reading should be about 30 parts per million.
The CO2 reading from the chart at the krib is more dependable than the CO2
test result. See below.
> have 3 neons, 3 checker barbs, 3 ottos, and 2 pearl gouramies which are doing
> fine. Plants are growing well also, but this morning I added a pair of blue
> rams which immediatly went to top gasping for air. Had to remove them to
> another tank for fear of killing them.
That's odd behavior. I don't see much reason to correlate it to CO2.
> Can anybody please tell me WHY IS MY
> CO2 SO HIGH AND WHY MY NUMBERS DO NOT CORRELATE WITH THE CHART NUMBERS? I
> only add one bubble per second of compressed Co2.
I checked the LaMotte web site. Their CO2 kit appears to be a simple
acidity test. What it actually measures is the concentration of acids
that will dissociate between the pH of your water sample and an endpoint
pH of 8.3 or so, when the indicator turns pink. Usually this is carbonic
acid (=dissolved CO2). It looks like your well water contains some other
weak acid that registers in the test as CO2, so the CO2 test is too
A very similar thing happens to KH tests. KH is usually caused entirely
by bicarbonate in the water, and the KH-pH-CO2 charts assume that it is
all bicarbonate. If there is something else in the water that registers
in the KH test then it will make the charts indicate a CO2 concentration
that is higher than it really is.
You have results from two tests, both of which can overestimate the actual
CO2 level. I don't know of any way for either test (when correctly
applied) to underestimate the CO2 level, so the lower of the two results
will always be closer to the right answer. The higher of the too results
can't be right. Ignore your high CO2 test results and keep in mind that
the CO2 result that you are getting off the pH-KH-CO2 charts are still a
high estimate of the actual CO2 concentration.
If I were you I'd really wonder what was in my water, and I'd make sure
I knew what, if anything, I'm adding to it.